1. Field of the Invention
The present invention relates to a blood pressure estimating apparatus and method for successively estimating an intraarterial blood pressure of a living subject, based on information non-invasively obtained from a circulatory organ of the subject.
2. Related Art Statement
There is known, as a blood pressure- measuring apparatus for non-invasively measuring an intraarterial blood pressure of a subject, a so-called Korotokoff-sound blood pressure measuring apparatus or oscillometric blood pressure measuring apparatus. The Korotokoff-sound blood pressure measuring apparatus determines a blood pressure of the subject, based on a pressing pressure of a pressing band being wound around a portion of the subject at the time of occurrence or disappearance of Korotokoff sounds produced by changing the pressing pressure of the pressing band. The oscillometric blood pressure measuring apparatus determines a blood pressure of the subject, based on variation of amplitude of a pulse wave produced while the pressing pressure of the pressing band is changed.
In an operating room, an intensive care unit, or the like, it is needed to successively measure a blood pressure of a subject when an urgent medical treatment or cure is required. In the case where the above conventional blood pressure measuring apparatus is used, it takes several tens of seconds from a start of the blood pressure measurement to obtain a blood pressure of the subject. Moreover, if an interval between successive blood pressure measurements is shortened to obtain a blood pressure at a relatively short period, congestion occurs to a body portion of the subject due to high frequency of pressing of the pressing band, whereby errors occur to the blood pressure measurements.
Further, there has been proposed a blood pressure estimating apparatus including means for calculating a velocity of propagation of a pulse wave which propagates through an artery of the subject, and means for successively estimating, according to a predetermined relationship between blood pressure and velocity of propagation of pulse wave, an intraarterial blood pressure of the subject, based on the calculated velocity of propagation of the pulse wave. An example of the blood pressure estimating apparatus is disclosed in Laid-open Publication No. 7-9305 of unexamined Japanese Utility Model Application and Laid-open Publication No. 7-308295 of unexamined Japanese Patent Application.
Thus, the above blood pressure estimating apparatus discloses only a technique to successively estimate the blood pressure based on a propagation time of a pulse wave or a propagation velocity of a pulse wave. In the case where the blood pressure is estimated based on only the pulse-wave propagation time or the pulse-wave propagation velocity, the blood pressure can not enjoy high accuracy. Therefore, it is needed to frequently calibrate the estimating apparatus, based on an actual blood pressure measured by the Korotokoff-sound blood pressure measuring apparatus or the oscillometric blood pressure measuring apparatus.